Underground Stormwater Storage with Structural Support Cells

August 17, 2015

Turning what most urban planners view as a threat into an opportunity is not easy. Extreme rainfall can have potentially catastrophic consequences – but they can also bring huge benefits if channeled properly. GreenBlue has invested many years into the research of urban tree development, and have designed proven systems to utilize stormwater and turn the threat of extreme weather events into a sustainable asset.

Last year’s Colfax Water Detention project on Colfax Street in Evanston, Illinois saw the GreenBlue StrataCell® system installed as a dry well for stormwater management in a Chicago suburb.

The property owner was building a new house in a neighborhood prone to flooding and wanted to ensure that the drainage plan was as aggressive as possible. The owner turned to Kettelkamp & Kettelkamp Landscape Architecture for recommendations on a more robust solution, who in turn suggested the use of StrataCells.

“The client wanted to ensure that the proposed civil engineering solution was aggressive enough for the amount of rainwater in his neighborhood,” explained landscape architect Claire Kettelkamp. “The 94% storage volume of the StrataCell provided an excellent solution for this residence.”

A zone under the front lawn of the property was selected for the storage area. The StrataCells were installed here to create a reservoir that would store excess stormwater and allow it to transport at a controlled rate. This provided the intended flood protection during the event of prolonged rainfall.

The pit location was 713 cubic feet, which provided ample space for the reservoir to ensure the drainage requirements. To accomplish the same storage volume with a stone mixture, it would have taken a pit approximately 2,160 cubic feet.

Due to the fact that StrataCells hold approximately three times more volume than the stone mixture that was initially intended for the project, the excavation zone was significantly condensed, which equated to notable cost savings.

This saving in excavation costs, in addition to the superior robustness of the method, is what persuaded the civil engineer to change his specification from a stone mixture to the StrataCell system.

When installing stormwater storage solutions in urban areas, engineers are often faced with a multitude of underground utilities and built infrastructure that can significantly complicate an otherwise straightforward installation. Due to the modularity of the StrataCell system, services can be easily accommodated through customized configurations. The skeletal matrix even allows for utilities to be integrated through the completed assembly.

GreenBlue StrataCells are structural support modules that are loadbearing for pedestrian and traffic areas. They have over 94% void space for tree root growth and/or stormwater storage. An example of a project where StrataCells have been utilized to repurpose the use of excess rainwater is the 2012 reconstruction of Mill Woods Sport Park in Edmonton, Alberta.

The detention system for this project was designed to function as a passive recreation facility for a small lake, which collects water and provides irrigation to the surrounding sports fields in the 40 hectare site.

The StrataCells were installed in a continuous trench along the center of the south parking lot to provide a filter / storage system for runoff water, and at the same time, provide soil volume for six trees installed within the matrix.

The water runoff drains into the center of the parking lot through permeable surfacing, then filtered and stored within the StrataCell system filled with washed rock. Once the water has filtered through the matrix, it reaches a perforated pipe, which is tied into the storm sewer and transferred to the stormwater lake located on the southeast side of the park. The perforated pipe continues beneath trees to transfer the water to the storm line.

These kind of stormwater management systems offer new opporunities to bring sustainability to the urban landscape. Learn more about stormwater management here.

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